Conventionally, internal combustion engines of one type in which fuel is injected into the inside of a combustion chamber, that is, internal combustion engines of the in-cylinder injection type, for example, have the distal end portion of a fuel injection valve inserted into and supported by an insertion hole of a cylinder head and have the proximal end portion of the fuel injection valve inserted into and supported by a delivery pipe (a fuel injection valve cup), whereby the fuel injection valve is provided across the cylinder head and the delivery pipe. When a fuel pressure supplied to the fuel injection valve through the delivery pipe has changed due to injection or stopping of the fuel, vibration based on the change in fuel pressure and vibration accompanying the operation of the fuel injection valve usually occur to the above fuel injection valve. For this reason, it is often the case that a vibration insulator to absorb and damp such vibration of a fuel injection valve is attached between the fuel injection valve and an insertion hole of a cylinder head.
On the other hand, the cylinder head and the delivery pipe are originally parts of separate bodies. Therefore, changes in the relative positions thereof, which are caused by, for example, tolerances associated with production or processing of these parts, tolerances associated with assembly in the production, thermal deformation, and various vibrations that accompany the operation of the internal combustion engine, are unavoidable. That is, the axis of the fuel injection valve provided across the cylinder head and the delivery pipe becomes inclined relative to the axis of the insertion hole of the cylinder head, whereby positions at which the fuel injection valve is supported by the cylinder head and the delivery pipe deviate from correct positions. Further, such positional deviation causes problems such as partial slack of an O-ring at the proximal end of the fuel injection valve, the O-ring serving to prevent fuel leakage between the fuel injection valve and the delivery pipe (fuel injection valve cup). Therefore, the positional deviation may possibly cause fuel leakage.
For this reason, insulators designed to not only absorb and damp vibration of the fuel injection valve but also reduce the influence of such inclination of the axis of the fuel injection valve have been proposed, and an insulator described in Patent Document 1 is known as one example thereof. The insulator described in Patent Document 1, as shown in FIG. 12, includes an annular adjustment element 60 sandwiched between a shoulder section 54 of a cylinder head 51 and a tapered stepped section 57 of a fuel injection valve 55, the diameter of which is enlarged in a tapered shape to face the shoulder section 54. While an injection nozzle 56 of the fuel injection valve 55 is arranged by being inserted into the insertion hole 52 (a receiving hole) of the cylinder head 51, the shoulder section 54 of the cylinder head 51 has an opening into a side wall 53 of the insertion hole 52. The adjustment element 60 has a first leg 61 extending along the shoulder section 54 of the insertion hole 52, and a second leg 62 extending along the tapered stepped section 57 of the fuel injection valve 55. Additionally, a structure elastically supporting the fuel injection valve 55 with respect to the cylinder head 51 is obtained by having the first leg 61 in surface contact with the shoulder section 54 of the insertion hole 52, and having the second leg 62 in surface contact with the tapered stepped section 57 of the fuel injection valve 55.
According to the thus configured insulator, even when the axis C2 of the fuel injection valve 55 has deviated from the centered position between the insertion hole 52 of the cylinder head 51 and a delivery pipe in assembly, the first leg 61 moves along the shoulder section 54 of the insertion hole 52 due to a force generated by the second leg 62, which flexes in accordance with the tapered stepped section 57 of the fuel injection valve 55. This serves to appropriately compensate the positional relations of the fuel injection valve 55 with the insertion hole 52 and the delivery pipe.
When the internal combustion engine is operated, a high pressing force based on the above described fuel pressure is applied to the second leg 62 of the adjustment element 60 through the tapered stepped section 57 of the fuel injection valve 55. At this time, a force toward the shoulder section 54 of the insertion hole 52 and a force toward the outer circumference of the adjustment element 60 are applied to the second leg 62 of the adjustment element 60 from the tapered stepped section 57 of the fuel injection valve 55 in a manner corresponding to the tapering angle of the tapered stepped section 57.